1. Field of the Invention
The present invention relates to machine tools. More particularly, this invention relates to an improved method and apparatus for automatically changing removable tool heads mounted on tool carrying unit. This invention has particular application to automatic machining units carrying a multi-spindle tool head for milling, drilling, tapping, boring or turning a workpiece held stationary at a work station, where the production rate of finished workpieces is advantageously at a low to medium production rate, approximately five to 30 finished pieces per machine per hour.
2. Description of the Prior Art
Other systems have been proposed for machining parts at the production rate of five to 30 finished pieces per hour. An automatic transfer machine could be used, but with its high capital cost is not economical for low or medium production.
A single-spindle, numerically-controlled machine is typically producing the finished workpieces where the production rate is up to five parts per hour range. A plurality of single-spindle, numerically controlled machines would be required to machine at the production rate of five to 30 finished pieces per hour. Such a plurality of machines requires a separate operator, a separate machine, and a separate floor space for each of the machines. Each machine is relatively slow, in that each tool must make multiple movements along the workpiece separately. Each machine also requires a separate workpiece setup. This system is expensive in terms of labor, capital and floor space, but has been used for the low and medium production machining for the lack of a suitable alternative.
Systems have been proposed which use multiple spindle tool heads with interchangeable tool heads. These systems are generally complex and cumbersome, frequently requiring considerable manipulation of the tool heads both into and out of the work station. Simultaneous movement of many tool heads required large forces to move the tool heads into the desired positions. The head changing process in these prior systems were slow, with the result that the machine time otherwise available for machining workpieces was spent instead nonproductively for changing tool heads.
The tool head changing machines of the prior art generally lack quick, precise positioning and alignment of the tool head with the tool carrier to provide a uniform seating of the tool head on the tool carrier.
Some tool head changing machines, such as U.S. Pat. No. 3,858,286 to Nohejl, lack means for cycling multiple tool heads to the tool carrier. Such a machine does not allow for rapid cycling of a plurality of tool heads.
In many prior art tool carrying machines, a single tool head is used at any one time, leaving the remainder of the tool heads idle. Considerable capital, invested in idle tool heads, would remain unused for a significant portion of the production time in such systems.